The present invention relates to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device that can improve the characteristics of a diffusion barrier and a method for forming the same.
Generally, aluminum (Al) and tungsten (W) are primarily used as a material for the metal line of a semiconductor device due to their good electrical conductivity. Recently, researches have been made offering copper (Cu) as a next-generation material for a metal line. Copper has excellent electrical conductivity and low resistance when compared to aluminum and tungsten. Therefore, copper can solve the problems associated with RC signal delay in the semiconductor device having a high level of integration and high operating speed.
Copper cannot be easily dry-etched into a wiring pattern. As a result, a damascene process is used in order to form a metal line using copper.
In the damascene process, a metal line made of copper is formed, such that a metal line forming region is defined by etching an insulation layer. A diffusion barrier is then deposited on the surface of the metal line forming region. Then, copper is completely filled into the metal line forming region.
Here, the diffusion barrier is usually formed as a double layer of TaN/Ta. A seed copper layer is formed on the diffusion barrier through PVD (physical vapor deposition) and the metal line forming region is filled with copper through electroplating using the copper layer as a seed layer.
However, limitations exist in forming the copper layer through PVD due to a low aspect ratio in a conventional semiconductor device below 40 nm as the size gradually decreases. Therefore, a method has been proposed that after forming a Ru layer through ALD (atomic layer deposition), a copper layer is formed through electroplating. The copper layer cannot sufficiently perform its function as a diffusion barrier however, since the TaN layer formed through ALD has a greater grain size than the TaN layer formed through PVD.
Also, the specific resistance of the TaN layer that is formed through ALD is very high to the extent of 500 μΩ·cm. The increase in the resistance of the entire metal line becomes substantial due to the presence of the TaN layer.
Meanwhile, the Ru layer formed on the TaN layer grows in a columnar shape. The Ru layer has the properties of a stable material that does not materially couple with copper. However, the diffusion barrier cannot perform properly since the Ru layer grows in a columnar shape.
Accordingly, in the copper metal line using the diffusion barrier as described above, the characteristics and reliability of the entire semiconductor device may be deteriorated since copper is likely to diffuse to the semiconductor substrate.